Current studies of the radioimmunoassay for ovine prolactin in plasma focus on the possible interference of metabolites of the endogenous molecule in the assay. Attempts to minic the sequential loss of immunoactivity seen previously in plasma measurements have not been successful with extracted ovine prolactin. The extracted ovine prolactin was used as either unlabeled or labeled additions to tissue incubates. A decapeptide sequence of the ovine prolactin molecule has been synthesized and its immunological behavior in the current radioimmunoassay and in its own radioimmunoassay is being studied.